1. Field of the Invention
The present invention relates to a conductive polymeric composite with a high electrical activation density and a method for preparing the same, and more particularly to a conductive polymeric composite with an increased electrical activation density obtained by compounding a ferrocene derivative having an electrical activity as a dopant with a polypyrrole of a conductive polymer and a method for making the same.
2. Description of the Prior Art
Known conductive polymers include polyacetylene, polypyrrole, polythiophene and etc. Such conductive polymers have not only a conduction property but also electrochemical characteristics such as an electrical discoloration characteristic and an oxidation and reduction characteristic. By virtue of these properties, they are widely used for various applications such as batteries, electrical discoloration display devices, photocells and etc. and the development thereof is being watched with keen interest.
In particular, polypyrrole, polythiophene and polyaniline can be produced by an electrochemical oxidation as well as a chemical polymerization using chemical oxidants and are known as materials exhibiting a high stability at room temperature. There have been issued various research articles and patents concerning these materials.
In spite of exhibiting superior electrical characteristics, nevertheless, these conventional conductive polymeric compounds are poor in workability, mechanical strength and stability. They also have a drawback of a low electrical activity density. As a result, such compounds encounter limitations on practical uses.
For solving the above-mentioned problems, many researches have been made so as to provide conductive polymeric compounds widely applicable to various technical fields. Examples of recently proposed methods are as follows.
As methods for solving the workability of conductive polymers, there have been disclosed a method for producing a conductive polymer by producing and processing a potential compound and heat treating the potential compound (Polymer, 1984, 25, 395), a method for compounding a conductive polymer with other polymeric resins (Polymer Commun., 1982, 23, 795), and a method for producing a composite by using paratoluene sulfonate as an electrolyte so as to enhance strength (IBM J. Res. Dev., 1983, 27, 342).
In particular, many research reports concerning improvements of electrolytic salts have been made, after a report was made about that conductive polymers could have a greatly improved mechanical strength, where an organic salt such as paratoluene sulfonate was used, in place of an inorganic salt such as lithium perchlorate.
However, most electrolytic salts newly proposed have no electrical activity in themselves. Therefore, when the electrolytic salts are compounded with conductive polymers having electrical activity, the density of electrically active material per volume is decreased, so that efficiencies of batteries, electrical discoloration display devices and etc. are degraded.
In particular, where these composites are used as electrode materials of secondary batteries, the electricity accumulation quantity of battery is greatly reduced, because of low density of electrically active material. Accordingly, the present inventors have made this invention capable of maintaining at a high level the density of electrically active material in a conductive polymeric composite obtained, by manufacturing a ferrocene derivative having an electrical activity in the form of an electrolytic salt to be used as a polymeric dopant.
There have been known several methods in which electrochemical active materials are used as electrolytic salts, to obtain conductive polymers. One of these methods is to manufacture polypyrrole or poly 3-methyl thiophene by using polyvalent anions such as PW.sub.12 O.sub.40.sup.3- SiW.sub.12 O.sub.40.sup.4-, and PMO.sub.12 O.sub.40.sup.3- obtained from oxides of tungsten and molybdenum. It has been known that in this case, electrochemical activity of polyvalent anions themselves is kept in the composites (E.H.Genies, Synth. Met,, 31 327 (1989) and T.Shimaidzu, J. Chem. Soc., Faraday Tran I, 84, 3941 (1988)).
Another method is to manufacture polypyrrole by using Prussian blue (Fe(CN).sub.6.sup.4- as an electrolyte (W.Breen, J. Electroanal. Chem., 297, 445 (1991)).
The electrolytes used in these methods were observed to have electrochemical activity and do stable and reversible oxidation-reduction reaction when they are compounded with conductive polymers. However, the conductive polymeric composites using the inorganic electrolytes in the form of monomers have a drawback that when the oxidation-reduction reaction is continuously carried out, the used electrolytes ace exuded, so that the repeated oxidation-reduction reaction can not be carried out.
This affects fatally the repetitive use life of secondary batteries and thereby makes it difficult to use the polymeric composites for practical purposes. That is, the extruded electrolytes may be a causes of sharply reducing the energy density of secondary battery after the charging and discharging operations of several ten times.
The method for manufacturing secondary batteries by using ferrocenes having electrochemical activity and their derivatives have been recently reported by Yoneyama and Kawai (Yoneyama, J. Electrochem. Soc., 134, 791 (1987) and Kawai, Electrochimica Acta., 34, 1357 (1989)). The Yoneyama's report disclosed that the secondary batteries obtained by using polyvinyl ferrocene have a high energy density of 126.4 mAh/g. The kawai's report disclosed that a secondary battery exhibiting superior charge efficiency and charging and discharging characteristics could be manufactured using polyvinyl ferrocene acetate, polyvinyl ferrocene sulfonate and polydimethyl vinylferrocene.
In cases of manufacturing a secondary battery by using such a ferrocene derivative alone, however, carbon powder of above 50% as a current corrector should be mixed with the ferrocene derivative, since the ferrocene itself has no electrical conductivity. As a result, there is a large loss in total energy density.